Batteries not included: How small-scale energy harvesting will power the future

The venerable crystal radio has been around since the early 1900s, but for one very unique reason, people still build and use them today. It isn’t particularly loud, it won’t grab faraway stations, and its esthetics certainly won’t impress your hoity-toity buddies. However, this old school marvel offers a single perk no other radio can: It functions without traditional power sources. That’s right – no cord, no batteries, no hamster wheels.

How is this possible? Because crystal radios grab all the power they need from the radio waves themselves.

Pretty cool, right?

Radio waves, you see, are energy. It works like this: Radio stations convert audio into radio waves that then travel, at the speed of light no less, omnidirectionally from the transmitter. These waves are, in essence, electromagnetic fields – forms of electrical energy not too dissimilar from the power that flows to your AC outlets, only they’re sprayed in all directions. The fractional amount that actually reaches your home is not very potent at all.

Bereft of other power sources, the crystal radio needs to “harvest” as much of the approaching electromagnetic field as possible. It does so with a rather considerable antenna (usually a long stretch of copper wire), a “coil” that’s tuned to the frequency (number of waves per second) of the desired station, a “detector” to extract the audio signal, and an earphone to convert the audio signal back into sound waves.

Though the crystal radio itself fell out of vogue some time ago, the “energy harvesting” part of the equation – whereby power is gobbled, both literally and figuratively, out of thin air – is now in the midst of a notable renaissance. From harnessing the frenetic energy of a dance club to utilizing the heat given off by the human body, engineers are looking to the world around us for untapped sources of energy. And getting results. Here’s why power outlets and batteries are no longer good enough, and what scientists are doing about it.

It’s all about our hunger for power. We begin our days operating various devices around our homes – alarm clocks, toasters, coffee pots. We then hop in our car, which itself has an unquenchable thirst for even more energy. Or maybe we grab the bus, toying with our notebook or tablet or smartphone or music player or handheld gaming system along the way. Ultimately, our entire day plays out as it began – dependent on various forms of electricity to do what we need to do.